Catalytic composition

ABSTRACT

By coating the internal surface of a cooking oven with a catalytic composition comprising porous mutually sintered vitreous enamel particles and finely divided transition metal oxides including copper oxide with the oxides of cobalt or manganese or both, the surfaces are rendered substantially selfcleaning. Preferred compositions are disclosed for situations in which (a) build-up of deposits is to be minimized, or (b) rapid removal of deposited fat is required.

United States Patent 1 Denny et al.

[ 51 Feb. 27, 1973 p CATALYTIC COMPOSITION [75] Inventors: Patrick JohnDenny; Dennis Albert Dowden, both of Stockton-on-Tees, England [73]Assignee: Imperial Chemical Limited, London, England [22] Filed: March29, 1971 [211 App]. No.: 128,684

Industries [52] US. Cl. ..l17/97, 117/23, 117/129, 117/160 R, 126/19 R,134/2 [51] Int. Cl. ..B44d 1/02 [58] Field of Search ..117/97, 129, 160R, 23; 126/19 R; 134/2 [56] References Cited UNITED STATES PATENTS3,547,098 12/1970 Lee .Q ..l26/l9R 3,549,419 12/1970 Stiles ..l34/23,576,667 4/1971 Lee 3,598,650 8/1971 Lee ..l34/2 PrimaryExaminer-Edward G. Whitby Attorney-Cushman, Darby & Cushman [5 7]ABSTRACT By coating the internal surface of a cooking oven with acatalytic composition comprising porous mutually sintered vitreousenamel particles and finely divided transition metal oxides includingcopper oxide with the oxides of cobalt or manganese or both, thesurfaces are rendered substantially self-cleaning. Preferredcompositions are disclosed for situations in which (a) build-up ofdeposits is to be minimized, or

(b) rapid removal of deposited fat is required.

9 Claims, 1 Drawing Figure PATENTED 3,718,498

who, MM

A ltorncys CATALYTIC COMPOSITION ovens is an old one and has led toattempts to develop a self-cleaning oven. Pyrolytic methods of achievingthis suffer from the disadvantage that they require the oven to beheated to a higher temperature than normal cooking temperatures in orderto burn off food residues.

Various catalytic methods of rendering an oven selfcleaning have beenattempted by coating the walls of the oven with an oxidizing catalystactive at about normal cooking temperatures. Considerable difficulty hasbeen encountered in finding a combination of metal oxides which whenmixed with glass frit and applied to the walls of an oven will form aporous layer which will have the desired hardness, abrasion resistanceand porosity without losing the effectiveness of the catalyst over aperiod of time in operation.

According to the present invention there is provided a cooking ovenhaving an internal surface coating comprising mutually sintered vitreousenamel particles and finely divided transition metal oxides includingcopper oxide with the oxides of cobalt or manganese or both.

By finely divided is meant a particle size well below 76 microns (i.e.,passing a 200 mesh BSS sieve) and typically below 25 microns, preferablybelow or even 2 microns. Such particles are made up of primaryparticles, which according to X-ray diffraction are of the order of 0.02microns in diameter, associated together in aggregates. A preferred wayof making them is described below.

The copper oxide proportion of the total of copper oxide and othertransition metal oxide or oxides is preferably at least percent by metalatoms. The proportions of the oxides depend on what degree ofselfcleaning is required. For avoiding build-up of fat decompositionproducts, mixtures containing at least 5 percent of cobalt oxide ormanganese oxide and lying within the area bounded by a line A passingthrough the points 30:65i5, :40:40 and 50:5:45, and more especiallymixtures lying within the area bounded by line B passing through thepoints 40:55 :5, 28:36:36, 40:20:40,

60:10:30 and 90:5:5, both on the triangular phase diagram for Cu:Co:Mn,are very suitable.

For effecting quick removal of fat and its decomposition products theproportion of manganese oxide is preferably greater, as represented bythe area bounded by line C passing through the points 10:10:90,10:30:60, 30:30:40, 45:20:35 and 60:0:40. Compositions in or near theregions of overlap of the areas A, B and C provide a useful combinationof both types of self-cleaning.

The coating preferably has a porosity in the range 5 to 50 volumepercent. It contains preferably l0-35 percent by wt. of the transitionmetal oxides. The particles of enamel may contain fused-in catalyticmaterial, but this is not necessary for the success of the invention.The coating may contain filling materials to improve porosity, forexample zinc oxide, alumina or magnesia. Other transition metals, ormetal oxides such as for example those of vanadium, iron, nickel,chromium, molybdenum, tungsten, niobium, tin or bismuth may be presentif desired.

The invention provides also a method of making the coated surface of theoven, which comprises forming a slip containing the mutually sinterablevitreous enamel particles and the finely divided transition metal oxidesincluding the oxide of copper with the oxide of cobalt or manganese orboth, applying it to a metal surface, drying it and calcining it toeffect mutual sintering of the enamel particles to the requiredporosity. A suitable calcining temperature is in the range 700800C forenamels affording a satisfactory combination of porosity and hardness.

The transition metal oxides are preferably prepared by co-precipitationfrom a solution of soluble salts preferably with a solution of an alkalimetal compound such as the carbonate. After washing, the precipitate iscalcined at a temperature sufficient to decompose the precipitate to themetal oxides, e.g., 400-600C, and ground if necessary to pass a 200 meshB.S.S. sieve. The oxides so produced usually require very littlegrinding and readily break into fine particles when shaken through thesieve. Aggregates passing the sieve are usually broken down further onstirring with the enamel slip.

The mixture of mutually sinterable enamel particles with the oxides ashereinbefore defined, whether in the dry state or aqueous slip state isbelieved to be a new composition of matter.

The invention is illustrated by the following examples:

EXAMPLE 1 A catalytic composition was prepared by dissolving 60.4 g. ofcupric nitrate trihydrate, 62.8 g. of manganous nitrate tetrahydrate and72.75 g. of cobalt nitrate hexahydrate in 750 ml. of distilled water at-85C, followed by the addition of a sodium carbonate solution at thesame temperature made by dissolving 79.5 g. of anhydrous sodiumcarbonate in 750 ml. of distilled water. The precipitate so obtained waswashed thoroughly with hot distilled water, then calcined at 600C for 2hours. After calcination the precipitate was ground by shaking through a200 mesh B.S.S. sieve to break up the few large aggregates present.

Five grams of the ground precipitate and 30g. of enamel slip containingabout 20 g. of solid material comprising enamel frit and additives weremixed with sufficient distilled water to produce a fluid paste. A sampleof this mixture was flow-coated on to a 7 X 7 cm. square piece of mildsteel which had been previously coated with a layer of vitreousnon-porous enamel ground coat. The coating was allowed to dry and washeated in an oven at 7 80-800C. The catalytic enamel coating whichresulted was about 0.03 cm. thick and was satisfactory in porosity,hardness and adhesion.

Material coated in this way was tested for its efficiency in removingquantities of lard deposited on its surface.

A drop (about 0.017 g.) of molten lard was deposited on a weighed 3 X 3cm. sample cut from the above coated steel sheet. This was heated in anoven at 225C for 24 hours, after which it was removed and reweighed inorder to calculate the weight loss of lard. Another drop of lard wasdeposited on the surface and the above were tested in a similar manner.

The results of these tests are shown in Table 1.

TABLE '1 Cumulative weight of lard residue on coating (grams) No. ofadditions of lard No Catalyst Commercially available of catalyst examplecatalyst 0 0 0 0 1 0.0042 0.001s 0.0028 2 0.0076 0.0021 0.0052 3 0.01040.0028 0.0072 4 0.0112 0.0027 0.0034 5 0.0132 0.0029 0.0095 6 0.01480.0030 0.0104 7 0.0169 0.0030 0.0120 8 0.0184 0.0030 0.0130 9 0.01970.0030 0.0136 10 0.0216 0.0030 0.0138

' It can be seen that, after the first two lard add1t1ons followed byheating, substantially the whole of subsequent additions was removedfrom the coating made according to the invention. In contrast, oncoatings made using no catalytic oxide or using the commerciallyavailable catalytic oven enamel, the lard residues continued to build upso as apparently to render the surface non-porous and catalyticallyinactive.

Similar results were obtained when similar lardtreated samples wereheated at 275C and in tests in which the lard was added every 3 hoursinstead of every 24 hours.

EXAMPLE 2 A catalytic composition was prepared as in Example 1, exceptthat the quantities of metal salts and sodium carbonate were adjusted soas to produce an oxide mixture having the composition 50 Cu: 25 Co: 25Mn by metal atoms. Two coated metal sheets were prepared, one of which(A) was heated at 780C, the other (B) at 720C, for 3 minutes. Theporosities of the coatings as measured by water absorption were 18percent for A and 27 percent for B.

When tested as in Example 1 the rate of build-up of Again, the build-upof lard residue had substantially ceased after the eighth drop, and thetotal residue was much less than that of the coating containing thecommercially available catalyst as set forth in Example 1.

EXAMPLE 3 A catalytic composition was prepared as in Example 1, exceptthat the quantities of ingredients were adjusted so as to produce anoxide mixture having the composition 20Cu: 20Coz60 Mn by metal atoms. Ametal sheet was flow-coated as before and heated at 780C for 3 minutes,to give an enamel layer of porosity 23 percent (Catalyst C).

When tested as in Example 1 the rate of build-up of residue was asfollows:

TABLE 3 No. of

additions of lard Cumulative weight of residue, grams EXAMPLE 4Comparison of catalysts A and C in test of initial rate of lard removalAfter application of lard to the previously weighed coated metal sheet,it was placed in an electric oven at 275C, then withdrawn and weighed atintervals. The weight of lard remaining was expressed as a percentage ofthe initial quantity and plotted on a graph against time. The initialrate was evaluated from the average slope of the curve between the startand the time required for removal of percent of the lard. Thepercentages removed and the initial'rates were as follows:

TABLE 4 TIME Percentage removal hours. Catalyst A Catalyst C 0 0 0 0.2521 36 0.5 34 56 0.75 47 67 1.0 54 1.5 76 81 2.0 85 84 3.0 88 87 4.0 9187 Initial rate per hour 61 It is evident that Catalyst C, containingmore manganese oxide and less copper oxide, provides a substantiallymore rapid initial removal of lard.

We claim:

1. A cooking oven having an internal surface coating comprising mutuallysintered vitreous enamel particles and, dispersed in said coating,particles of finely divided transition metal oxides including copperoxide in admixture with the oxide of cobalt or manganese or both.

2. An oven according to claim 1 in which the oxides have an averageparticle size up to microns.

3. An ovenaccording to claim 1 in which the copper oxide constitutes atleast percent of the oxides by metal atoms.

4. A cooking oven especially adapted to avoid buildup of fatdecomposition products, said oven having an internal surface coatingcomprising mutually sintered vitreous enamel particles and finelydivided transition metal oxides including copper oxide in admixture withthe oxide of cobalt or manganese or both, said oxide mixture containingat least 5 percent of cobalt oxide or of manganese oxide and lyingwithin an area bounded by line A on the accompanying triangular phasediagram.

companying triangular phase diagram.

6. A cooking oven especially adapted for quick removal of fat and itsdecomposition products, said oven having an internal surface coatingcomprising mutually sintered vitreous enamel particles and finelydivided transition metal oxides including copper oxide in admixture withthe oxide of cobalt or manganese or both, said oxide mixture lying inthe area bounded by line C on the accompanying triangular phase diagram.

7. An oven according to claim 1 in which the coating has a porosity inthe range 5 to 50 volume percent.

8. An oven according to claim 1 in which the coating contains 10-35percent by weight of transition metal oxides.

9. An oven according to claim 1 in which the transition metal oxides ofthe coating have been prepared by co-precipitation.

2. An oven according to claim 1 in which the oxides have an averageparticle size up to 10 microns.
 3. An oven according to claim 1 in whichthe copper oxide constitutes at least 15 percent of the oxides by metalatoms.
 4. A cooking oven especially adapted to avoid build-up of fatdecomposition products, said oven having an internal surface coatingcomprising mutually sintered vitreous enamel particles and finelydivided transition metal oxides including copper oxide in admixture withthe oxide of cobalt or manganese or both, said oxide mixture containingat least 5 percent of cobalt oxide or of manganese oxide and lyingwithin an area bounded by line A on the accompanying triangular phasediagram.
 5. An oven according to claim 4 in which the oxide mixture lieswithin an area bounded by line B on the accompanying triangular phasediagram.
 6. A cooking oven especially adapted for quick removal of fatand its decomposition products, said oven having an internal surfacecoating comprising mutually sintered vitreous enamel particles andfinely divided transition metal oxides including copper oxide inadmixture with the oxide of cobalt or manganese or both, said oxidemixture lying in the area bounded by line C on the accompanyingtriangular phase diagram.
 7. An oven according to claim 1 in which thecoating has a porosity in the range 5 to 50 volume percent.
 8. An ovenaccording to claim 1 in which the coating contains 10-35 percent byweight of transition metal oxides.
 9. An oven according to claim 1 inwhich the transition metal oxides of the coating have been prepared byco-precipitation.